1. Field of the Invention
The present invention relates to an apparatus for recording signals such as image signals on a disk recording medium and, more particularly, to control of management information of recorded signals.
2. Related Background Art
Conventionally, a video tape recorder which records analog video signals on magnetic tapes is available as an image recording apparatus for recording video signals on a recording medium. However, with rapid progress of digital signal processing technologies, digital recording/playback apparatuses which record analog video signals on a recording medium by converting the signals into digital video signals are becoming popular at present.
Such digital recording/playback apparatuses include a digital VTR, a digital video disk apparatus which records signals on a solid-state disk or magnetooptical disk, and a solid-state memory video apparatus which records signals in a solid-state memory such as a flash memory or an SRAM.
These digital recording/playback apparatuses load a video signal obtained by an image pickup device such as a CCD and convert the signal into a digital signal by A/D conversion. The apparatuses reduce the information amount by compression-encoding this digital video signal. In this manner, these apparatuses can record a large amount of image information in a small recording capacity.
Schemes used as this compression encoding are discrete cosine transform (to be referred to as DCT hereinafter) which is orthogonal transformation having the highest compression efficiency, and a variable-length coding scheme. To perform compression encoding, a single image is first segmented into a plurality of blocks each having x horizontal pixels and y vertical pixels, and DCT transform is performed for each block. A DCT coefficient after the transform is divided by a certain divisor, and the remainder is rounded, thereby performing quantization. By using the characteristic that a quantized image is concentrated in low-frequency components, the number of bits of high-frequency components is reduced. In this way, the information amount is greatly reduced.
The information amount can be further compressed by performing variable-length encoding, e.g., Huffman coding, which assigns to the quantized data a code length corresponding to the occurrence frequency of the data.
Furthermore, greater compression can be attained by combining interframe predictive encoding which calculates the difference between frames, by using the characteristic that a motion image has a strong correlation between frames.
Of this type of recording/playback apparatuses, the capacities of disk media of disk apparatuses are rapidly increasing in recent years. Consequently, apparatuses which record and play not only audio signals but video signals in and from a disk medium for a long time have been proposed. For example, a technique has been proposed which uses a recording format based on high-efficiency encoding such as MPEG using, e.g., DCT and variable-length encoding described above, and which can realize a recording/playback apparatus which records video signals for one hour or more at data rates of about 4 Mbps and 10 Mbps. Furthermore, disk media themselves are being reliably decreased in size and increased in capacity.
In an image recording apparatus which records video signals on a disk medium by reducing the information amount by compressing the signals by combining the aforementioned compression techniques, the information amount varies in accordance with an image because variable-length encoding is used. Therefore, a rate control means for holding the information amount constant is used to uniformize the recording rate of images, thereby recording images in a predetermined recording media capacity within a predetermined time.
This rate control uniformizes the rate by writing compressed data having variations into a certain predetermined buffer and reading out the data at a constant rate. That is, buffer control is performed such that if the data may exceed a predetermined value of the buffer, the quantization level described above is increased to raise the compression ratio; if the buffer does not satisfy the predetermined value, the quantization level is decreased to lower the compression ratio.
In constant bit rate recording (CBR recording), the recording rate is held constant by giving priority to the target time of recording on a recording medium. Hence, if an input image moves fast or has a wide color band, quantization becomes coarse to make the image nonuniform between frames. Therefore, an image recording apparatus which performs variable bit rate recording (VBR recording) by attaching importance to image quality has been proposed. This VBR recording performs encoding giving priority to image quality by holding the quantization level of recording at a substantially constant value, while allowing fluctuations of the recording rate.
A recording/playback apparatus like this uses management information called Table of Contents (to be referred to as a TOC hereinafter) to control video data recording and playback operations. When video data obtained by image pickup is recorded on a recording medium, the TOC information is recorded in an area formed on the inner peripheral side of the disk medium independently of an area for recording video data. In playback operation, the TOC information is read out from the disk medium and held in an internal memory of the apparatus. On the basis of this TOC information, the position of access to the disk medium and diverse operations such as video data playback management are controlled.
Examples of operations managed using the TOC are an operation of linking data of one scene, which are discontinuously recorded on a recording medium, and continuously displaying back the data, an operation of deleting a scene once obtained by image pickup, and an operation of recording a scene newly obtained by image pickup in a free space formed by deletion.
In any of these operations, video data is recorded in an area (video recording area) formed near the center in the radial direction of a disk medium, and the TOC information is saved in an area (system information management area) formed inside the image recording area. Note that no data can be recorded in the outer periphery of the disk.
Since the TOC is important information necessary to recording/playback, the reliability is improved by, e.g., recording the TOC a plurality of times in the system management area of a disk.
In conventional image pickup recording/playback apparatuses, the TOC is recorded on a disk after video data is completely written in the medium. That is, after the recording end pointer (address) of video data on a disk is determined, various pieces of information including an end pointer and start pointer are recorded as the TOC information.
If, therefore, one recorded scene extends over a long time period, no TOC information may be recorded for long periods of time.
Also, a system using a disk medium can rapidly access data in the disk medium, so recording or playback access to the disk medium is usually intermittently performed. Between this disk access operation and other operations, large differences are produced in consumption power such as motor driving power, head driving power, and write laser power.
When a series of recording operations are performed with battery driving, therefore, the battery supply voltage lowers with an abrupt rise of the consumption power upon disk access. This sometimes makes the recording operations of the system impossible to perform.
Especially when the TOC information is to be recorded, the write operation is performed by moving a recording/playback head mechanism from the video recording area for recording video data to the system management area in a remote position. Hence, if the battery amount remains to such an extent that a video data recording operation is marginally possible, the TOC information cannot be written in the worst case.
If the TOC information is missing, the start pointer, end pointer, attribution, and the like of recorded video data are unknown, so disk medium playback control cannot be performed.
Also, even if the reliability of the TOC data is improved as described previously, recording is sometimes abnormally terminated in the middle of a scene by, e.g., careless handling by a user, running out or abrupt discharge of a battery, a defect of a recording medium, or some external cause. In a case like this, actually recorded images and sounds and additional data sometimes disagree with the contents of the TOC. This makes playback of the scene based on the TOC impossible.